I think the intent is good to provide a safe place for kids. However, there are too many pices of the puzzle missing. First, does anyone have a browser tha ONLY get's kids.us domains? No, so creating a safe place for kids with a bus that will let them of at the strip joint does very little.
To filter eveything but .kids.us takes special software. If you actually use it to allow white listed domains, actually works fairly well. Once you have that, you might as welll allow visiting disney.com or nickelodeon.com which then makes .kids a moot point.
I think a safe haven for kids will come with IPv6. I would propose that IP's be handed out by country (for cutltural reasons) and by type of use. Different ranges could be given out for standard ratings like the movies, so that domains would not be necessary , and blocking could be done by ip range. Right now, it's way too easy to move, forward, park and point domains to make real and accurate filtering. Same holds true with email and trying to control by content or domains.
Kids.us has too many limitations to make it useful on todays internet. No outgoing links, no email addresses, not two way contact, limited to no user to user contact like this forum, etc.